Method of making electric contact plugs



July 13,1948. H LOVESEY METHOD OF MAKING ELECTRIC CONTACT PLUGS FiledApril 2. 1946 'ing ring Patented July 13, 1948 METHOD OF -MAKINGELECTRIC I I CONTACT PLUGS Horace Lovesey,

London, "England, assignor to Telephone Manu'facturing 'Company Limited,

London, England Application April 2,1946,?Serial N 0.659.022 InGrcat'Britain April .13, .1945

Thepresent invention relates to contact plugsand the like comprising twoor more elongated elements assembled coaxially one within the other, thesaid elements being separated by insulating material.

The present invention has for its object the provision of improvementsin a device such as a contact plug or the like and in the manufacturethereof, and, according tothe invention,-an inner element thereof has aseparating and locatof insulating material'initially moulded on it ofsuch size that it can be located within the tubular bore of the nextlarger element, and, when the elements are then held into their properrelationship, the remaining insulating material is injected.

The invention is particularly applicable to telephone jack plugs of thetip, ring and sleeve type consisting of an inner rod mounted coaxiallywithin an inner sleeve which in turn is mounted coaxially within anouter sleeve. The inner rod at its forward end projects beyond theforward end of the inner sleeve and has an annular contact on itsprojecting end. The inner sleeve at its forward end projects beyond theforward end of the outer sleeve. Ihe three elements are separated byinsulating material and the ring on the forward end of the inner rodforms the tip contact; the projecting end of the inner sleeve forms thering contact and the outer sleeve forms the sleeve contact.

In making a plug of this kind it is convenient to insert the insulatingmaterial by injection of a thermoplastic or thermo-setting insulation,but this may result in faulty plugs, due to the conducting elementsbeing displaced. While jigs may be employed during the injection toreduce the displacement it is still diflicult to ensure that theelements, especially the central rod and the inner sleeve are correctlyaligned and insulated. With the present invention this defect can besubstantially eliminated.

In the accompanying drawing is shown by way of example stages in theassembly of a telephone jack plug of the tip, ring and sleeve type. Inthis drawing Figure 1 is an elevation of the inner element;

Figure 2 is a section of the inner element located within the firstsleeve;

Figure 3 is a section of both the elements of Figure 2 located withinthe outer sleeve before the insulating material is inserted; and

Figure 4 shows the plug with insulating material inserted, and with thecontacts shaped to standard profile.

'tral'ro'd I is located In this embodiment of the invention'the'cenwithin the inner sleeve 2, which in turni's arranged.- withinthe outer sleeve 3. .The rod I'is stamped or otherwise formed at its oneend with longitudinal .grooves 4 in'two parts, with an ungrooved portion5 between .them of slightly reduced diameter. "At its other end the rodis formed with an off-set portion 6 with a threaded hole "I therein.

After the rod I has been shaped as described, a small insulating'locatorring 8 is moulded on to the rod,'the external diameter of the ring beingequal'to'the internaldiameter of the innersleeve 2. To assist insecuring this ring uponthe rod a small nick may be made at 9.

The rod I after the ring 8 is moulded thereon,

is positioned within the inner sleeve 2 and a Washer I0 of hardinsulating material is placed over that end of the rod which projectsthrough the sleeve. A brass or other suitable collar II is then forcedon to the grooves 4 and deformed by crimping at I2 to grip in theportion 5 of the rod between the grooves, thus securely holding thecollar on the shaft. The ring 8 will fit closely within the sleeve 2,and to assist in securing this fit the ring may be moulded in a two-partmould, when the "flash formed at the junction of the two parts willprovide two high spots which will give a good frictional fit in thesleeve.

The inner sleeve 2 is cut away at I3 in the usual manner to give accessto the rear end of the rod I, and is .provided with a threaded hole I4at its rear end. The sleeve also has a stepped portion I5 at its forwardend which eventually provides the ring contact of the plug, and the endface I6 of this stepped portion is serrated or otherwise roughened. Theouter end of the bore of the sleeve 2 may be tapered as shown at IT.

The rod I and inner sleeve 2 as assembled are next inserted in the outersleeve 3. As is usual,

I sleeve 3 is cut away as at I8, to give access to the ends of sleeve 2and rod I. The parts are then mounted in a moulding die, pins, orpreferably screws, being inserted in holes 1 and I4 in the members I and2. In addition the sleeve 3 and the forward end of sleeve 2 are locatedin the die; the stepped portion l5 on the sleeve 2 enables this to bedone accurately.

When the parts are correctly positioned insulating material I9 isinjected into the mould, and allowed to harden; it will be apparent thatif this process involves heat, as is usually the case, the material ofthe ring must be such as not to soften at the temperatures involved. Inthis moulding the parts of the plug are firmly held and the obstructioncaused by the locating ring 8" i will be negligible. The high spotscaused by the moulding flash will leave a small gap for material to passthrough; if this is found to be insufficient the locator ring may beformed; with a groove or grooves or may be otherwise shaped tofacilitate the flow of the material past the ring.

The plug is completed by cleaning and shaping 7 the tip and ringportions to a standard profile,

as shown in Figure 4, and an outer insulating What I claim and desire tosecure by Letters Patent is:

Method of manufacturing a contact plug of the type comprising a centralrod terminating in a tip contact, an inner conductive sleeve surroundingsaid rod and terminating in a contact ring, and an outer conductivesleeve surrounding said inner sleeve and constituting a contact sleeve,said method including the steps of molding a short cylindrical insulatoronto said rod of a diameter substantially equal to the inner diameter ofsaid inner sleeve to provide a close friction fit therebetween, slidingsaid inner sleeve in place on said rod over said insulator to provide asub-assembly of said rod and inner sleeve, positioning said sub-assemblyand outer sleeve in place inside a mold, and injecting insulating case20 is slipped over the sleeve 3 in the usual" manner. 7

In this description of one embodiment of the invention reference hasbeen made to the use of one ring 8 of insulating material for holdingthe parts in position prior to moulding, but it will be understood thatmore than one ring may be used if necessary. With the arrangement shownand described, however, we have found that the one ring 8 is sufficientto ensure that the number of reject plugs due to misalignment or shortcircuits between adjacent members isaminimum. It is desirable to use theminimum number of rings, as the obstruction to the injected mouldedmaterial is then minimized.

plastic-material into the mold to fill the annular voids between saidrod and inner sleeve and between said inner and outer sleeves.

I HORACE LOVESEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Brunetti Apr. 16, 1940

